In the earlier games, each Copy Power only had one or two types of attacks. Newer ones like in Super Star had a whole list of them. I know this is going to be obvious, but which do you like better?
I prefer complex. More moves means better powers. But it does take a while to remember them all, especially with stuff like Fighter in KSS(>10 different attacks?!)
Enemies should also have health bars. Dying in one hit gets old.